detail of sexual reproduction in plants
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Plant reproductive morphology is the study of the physical form and structure (the morphology) of those parts of plants directly or indirectly concerned with sexual reproduction.
Close-up of a flower of Schlumbergera (Christmas or Holiday Cactus), showing part of the gynoecium (the stigma and part of the style is visible) and the stamens that surround it
Among all living organisms, flowers, which are the reproductive structures of angiosperms, are the most varied physically and show a correspondingly great diversity in methods of reproduction. Plants that are not flowering plants (green algae, mosses, liverworts, hornworts, ferns and gymnosperms such as conifers) also have complex interplays between morphological adaptation and environmental factors in their sexual reproduction. The breeding system, or how the sperm from one plant fertilizes the ovum of another, depends on the reproductive morphology, and is the single most important determinant of the genetic structure of nonclonal plant populations. Christian Konrad Sprengel (1793) studied the reproduction of flowering plants and for the first time it was understood that the pollination process involved both biotic and abiotic interactions. Charles Darwin's theories of natural selection utilized this work to build his theory of evolution, which includes analysis of the coevolution of flowers and their insectpollinators.
Use of sexual terminology
Dioicous gametophytes of the liverwort Marchantia polymorpha. In this species, gametes are produced on different plants on umbrella-shaped gametophores with different morphologies. The radiating arms of female gameteophores (left) protect archegonia that produce eggs. Male gametophores (right) are topped with antheridia that produce sperm.
Plants have a complex lifecycle involving alternation of generations. One generation, the sporophyte, gives rise to the next generation via spores. Spores may come in different sizes (microspores and megaspores), but strictly speaking, spores and sporophytes are neither male nor female. The alternate generation, the gametophyte, produces eggs and sperm. A gametophyte can be either female (producing eggs), male (producing sperm) or hermaphrodite (monoicous, producing both eggs and sperm).
In groups like liverworts, mosses and hornworts, the dominant generation is the sexual gametophyte. In ferns and seed plants (including cycads, conifers, flowering plants, etc.) the sporophyte is by far the most dominant generation. The obvious visible plant, whether a small herb or a large tree, is the sporophyte, and the gametophyte is very small. In seed plants, the female gametophyte, and the spores that give rise to it, are hidden within the sporophyte and are entirely dependent on it for nutrition. The male gametophyte consists of a few cells within a pollen grain.
The sporophyte of a flowering plant is often described using sexual terms (e.g. "female" or "male") based on the sexuality of the gametophyte it gives rise to. For example, a sporophyte that produces spores that give rise only to male gametophytes may be described as "male", even though the sporophyte itself is asexual, producing only spores. Similarly, flowers produced by the sporophyte may be described as "unisexual" or "bisexual", meaning that they give rise to either one sex of gametophyte or both sexes of gametophyte.
Flowering plants
Basic flower morphology
Flower of Ranunculus glaberrimus
The flower is the characteristic structure concerned with sexual reproduction in flowering plants (angiosperms). Flowers vary enormously in their construction (morphology). A "complete" flower, like that of Ranunculus glaberrimus shown in the figure, has a calyx of outer sepals and a corolla of inner petals. (The sepals and petals together form the perianth.) Next inwards there are numerous stamens, which produce pollen grains, each containing a microscopic male gametophyte. Finally in the middle there are partially joined carpels, which at maturity contain ovules, and within the ovules are tiny female gametophytes. Each carpel in Ranunculus species produces one ovule,which when fertilized becomes a seed.
Stamens may be called the "male" parts of a flower; collectively they form the androecium. Carpels may be called the "female" parts of a flower; collectively they form the gynoecium. The carpels are often fused together to varying degrees; the entire structure may be called a pistil. The lower part of the carpel or of the fused pistil, where the ovules are produced, is called the ovary; it may be divided into chambers (locules) corresponding to the separate carpels.
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Close-up of a flower of Schlumbergera (Christmas or Holiday Cactus), showing part of the gynoecium (the stigma and part of the style is visible) and the stamens that surround it
Among all living organisms, flowers, which are the reproductive structures of angiosperms, are the most varied physically and show a correspondingly great diversity in methods of reproduction. Plants that are not flowering plants (green algae, mosses, liverworts, hornworts, ferns and gymnosperms such as conifers) also have complex interplays between morphological adaptation and environmental factors in their sexual reproduction. The breeding system, or how the sperm from one plant fertilizes the ovum of another, depends on the reproductive morphology, and is the single most important determinant of the genetic structure of nonclonal plant populations. Christian Konrad Sprengel (1793) studied the reproduction of flowering plants and for the first time it was understood that the pollination process involved both biotic and abiotic interactions. Charles Darwin's theories of natural selection utilized this work to build his theory of evolution, which includes analysis of the coevolution of flowers and their insectpollinators.
Use of sexual terminology
Dioicous gametophytes of the liverwort Marchantia polymorpha. In this species, gametes are produced on different plants on umbrella-shaped gametophores with different morphologies. The radiating arms of female gameteophores (left) protect archegonia that produce eggs. Male gametophores (right) are topped with antheridia that produce sperm.
Plants have a complex lifecycle involving alternation of generations. One generation, the sporophyte, gives rise to the next generation via spores. Spores may come in different sizes (microspores and megaspores), but strictly speaking, spores and sporophytes are neither male nor female. The alternate generation, the gametophyte, produces eggs and sperm. A gametophyte can be either female (producing eggs), male (producing sperm) or hermaphrodite (monoicous, producing both eggs and sperm).
In groups like liverworts, mosses and hornworts, the dominant generation is the sexual gametophyte. In ferns and seed plants (including cycads, conifers, flowering plants, etc.) the sporophyte is by far the most dominant generation. The obvious visible plant, whether a small herb or a large tree, is the sporophyte, and the gametophyte is very small. In seed plants, the female gametophyte, and the spores that give rise to it, are hidden within the sporophyte and are entirely dependent on it for nutrition. The male gametophyte consists of a few cells within a pollen grain.
The sporophyte of a flowering plant is often described using sexual terms (e.g. "female" or "male") based on the sexuality of the gametophyte it gives rise to. For example, a sporophyte that produces spores that give rise only to male gametophytes may be described as "male", even though the sporophyte itself is asexual, producing only spores. Similarly, flowers produced by the sporophyte may be described as "unisexual" or "bisexual", meaning that they give rise to either one sex of gametophyte or both sexes of gametophyte.
Flowering plants
Basic flower morphology
Flower of Ranunculus glaberrimus
The flower is the characteristic structure concerned with sexual reproduction in flowering plants (angiosperms). Flowers vary enormously in their construction (morphology). A "complete" flower, like that of Ranunculus glaberrimus shown in the figure, has a calyx of outer sepals and a corolla of inner petals. (The sepals and petals together form the perianth.) Next inwards there are numerous stamens, which produce pollen grains, each containing a microscopic male gametophyte. Finally in the middle there are partially joined carpels, which at maturity contain ovules, and within the ovules are tiny female gametophytes. Each carpel in Ranunculus species produces one ovule,which when fertilized becomes a seed.
Stamens may be called the "male" parts of a flower; collectively they form the androecium. Carpels may be called the "female" parts of a flower; collectively they form the gynoecium. The carpels are often fused together to varying degrees; the entire structure may be called a pistil. The lower part of the carpel or of the fused pistil, where the ovules are produced, is called the ovary; it may be divided into chambers (locules) corresponding to the separate carpels.
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